It is inherently a problem of the two-stroke internal-combustion engine that it is inefficient and has inconsistent torque and power delivery. It can be said that most if not all exhaust pipes for two-stroke engines produce a narrow power band width and are RPM related. Because of these problems, use of the relatively simple two-stroke engine has fallen from the favor of many vehicle manufacturers.
The commonly used continuous-diameter exhaust pipe merely allows for the convenient exit of exhaust from a two-cycle engine. It is well known and accepted by those skilled in the art that the two stroke engine performance can be greatly improved with the assistance of a tuned exhaust system. If properly designed and constructed, a two-stroke exhaust pipe can improve the volumetric efficiency of an engine by scavenging the initial outward-bound gas flow (by use of a diffusing shape to assist in the evacuation of the flow), and after a transitional flow, by temporarily plugging this outward exhaust gas flow (by use of a returning pressure wave created by the shape of a reflector cone) as it attempts to exit the pipe. Depending on the potential of a given two-stroke engine, the improvement can be as great as 15 to 20%.
Additional improvements to exhaust systems have led to the development of the expansion chamber as part of the exhaust system. Most important to the super charging of the engine with an expansion chamber is the amount of improvement and the resulting power band width. It is well known and accepted that the geometric shape of the expansion chamber is very important in achieving optimum performance. Typically, the expansion chamber is shaped to look like a trumpet through the first stage, followed by a single parallel can-shape for a dwell period in the second or transition stage, and finally a reverse cone (funnel-shape) at the output end. The expansion chamber may contain single or multiple expansion cones, transition areas, and reflector cones, which improve torque and power and efficiency. However, current designs that have achieved improved high levels of torque and power and/or efficiency result in bulky exhaust systems consisting of multiple, individual, stand-alone and ultimately-joined pipes with expansion chambers of differing dimensions, serving one piston, cylinder and one combustion chamber. They have achieved these levels by use of primary, secondary, and in some cases, tertiary expansion chambers not contained within one another. Some such systems have commonly-joined partitioned walls or commonly-joined but partially open walls, but again, they are not contained one within the other. See for example, Gilbertson U.S. Pat. Nos. 6,134,885 and 6,381,956. Ultimately, such systems must join their multiple expansion chambers to a single, central location, serving as an entry for the exhaust gases leaving an engine's cylinder. While these systems achieve attainable levels of torque, power and efficiency for a high performance exhaust system, the resulting structures do not meet the available space requirements of vehicle manufacturers. Thus, it has proven difficult for a designer to achieve the maximum potentials of torque and power and efficiency throughout the entire RPM range of said engines while employing the torque and power-enhancing concept of an expansion chamber within the confines of a compact unit. Moreover, in order to satisfy these design requirements, the cross sectional area at each point along the exhaust pipe needs be maintained, and the inside of the exhaust pipe needs to be free from obstructions.
There have been other attempts to achieve the goal of maximum potential or torque, power and efficiency in a compact unit by adding a single reflective cone inside the exhaust pipe, which cone extends from the outlet end and terminates just at the center or transition section. An example of such a structure is shown in Richardson U.S. Pat. No. 3,786,791. Although this structure improves somewhat the torque and efficiency without requiring additional space, it does not achieve the maximum potential possible with the use of expansion chambers in an exhaust system.
There is, therefore, a need for an improved exhaust system for two-stroke internal combustions engines that will achieve more efficient and consistent torque and power delivery throughout the RPM range of the engine while satisfying the limited space requirements desired by most vehicle manufacturers.